A method and a corresponding dual-source CT device for performing the method is generally known and is often used if an optimally high time resolution is desired during a CT scan, for example in order to create tomographic images of a beating heart.
The ECG-triggered sequence mode is a very common, dose-efficient technique for examining the heart by way of a dual-source CT device. With this examination technique the ECG signal from the patient is used to trigger axial scans without couch movement using two measurement systems in a user-selectable cardiac phase of the patient, preferably in the low-movement end-diastolic phase. Following such an axial scan the patient couch moves to the next examination position where, again triggered by the patient's ECG, the next axial scan is performed. The examination volume covered in a single axial scan roughly corresponds to the width of the two detectors (of equal width according to the prior art) in the rotation center of the CT system, reduced by an overlap region of about 10% which is necessary for the image reconstruction. The width of the detector is therefore measured in the system axis direction or also the z direction of the CT system, i.e. in the longitudinal direction of the patient.
With a dual-source CT device having two detectors with for example 64×0.6 mm collimation each, corresponding to a width in the z direction of 38.4 mm, the covered volume per axial scan is about 35 mm. For examination of the entire heart volume of about 12 cm extension in the z direction, four axial scans as an example are required with such a device. The time resolution of the images produced with this scan mode is therefore about a quarter of the rotation time of the dual-source CT device when the simultaneously recorded data of the two detectors is taken into account.
It is desirable to reduce the number of individual scans for imaging the heart volume, i.e. to have to perform for example only two individual axial scans in future instead of four. The total examination time is reduced as a result. Fewer cardiac periods would therefore contribute to the image and the risk of image quality problems, for example due to the changing contrast agent concentration throughout the overall examination period or the changing heart rate of the patient, would be lower.